1. Field of the Invention
The present invention in the fields of molecular biology, immunology and medicine relates to a chimeric nucleic acid, including DNA and viral RNA encoding a fusion protein and its use as a vaccine to enhance immune responses, primarily cytotoxic T lymphocyte (CTL) responses to specific antigens such as tumor or viral antigens. The fusion protein comprises an antigenic polypeptide fused to a protein that promotes intercellular transport and processing via the MHC class I pathway, such as the VP22 protein from herpes simples virus and related herpes viruses.
2. Description of the Background Art
Naked DNA vaccines have emerged as attractive approaches for vaccine development (for review, see (1-3)). Intradermal administration of DNA vaccines via gene gun represents a convenient way of delivering DNA vaccines into professional antigen presenting cells (APCs) in vivo. Professional APCs are a superior candidate for mediating presentation of an antigen encoded by such a DNA vaccine to T lymphocytes of the immune system. The “gene gun” strategy provides efficient delivery of DNA into epidermal bone marrow-derived APCs termed Langerhans cells, which move to draining lymph nodes where they enter the lymphatic system (Condon et al., 1996). The present inventors and their colleagues have successfully used this system of DNA delivery to test various intracellular targeting strategies (Chen et al., 2000; Ji et al., 1999); co-pending, commonly assigned U.S. patent applications U.S. Ser. Nos. 09/421,608; 09/501,097, 09/693,450 and 60/281,003).
However, one limitation of DNA vaccines is their potency, since they do not have the intrinsic ability to amplify and spread in vivo as some replicating viral vaccine vectors do. The present inventors conceived a strategy that facilitates the spread of antigen may significantly enhance the potency of naked DNA vaccines.
VP22, a herpes simplex virus (HSV-1) protein has demonstrated the remarkable property of intercellular transport and is capable of distributing protein to many surrounding cells (4) (U.S. Pat. No. 6,017,735, O'Hare & Elliott, 25 Jan. 2000). For example, VP22 has been linked to p53 (Phelan, A. et al., 1998, Nat Biotechnol 16:440-3) or thymidine kinase (Dilber, M S et al., 1999, Gene Ther 6:12-21), facilitating the spread of linked proteins to surrounding cells in vitro and the treatment of model tumors.
Marek's disease virus type 1 (MDV-1) UL49 shares homology with HSV-1 VP22 (Koptidesova et al., 1995, Arch Virol. 140, 355-362) and has been shown to be capable of intercellular transport after exogenous application (Dorange et al., 2000, J Gen Virol. 81 Pt 9, 2219-2230).
Recently, self-replicating RNA vaccines (RNA replicons) have also emerged as an important strategy to enhance the potency of nucleic acid vaccines for cancer immunotherapy (for review, see Leitner, W et al., 1999, Vaccine 18:765-777. RNA replicon vaccines may be derived from alphavirus vectors, such as Sindbis virus (Hariharan, J M et al., 1998, J. Virol. 72:950-958), Semliki Forest virus (Berglund, P et al., 1997, AIDS Res. Hum. Retrovir. 13:1487-1495; Berglund, P. et al., 1998, Nat. Biotech. 16:562-565) or Venezuelan equine encephalitis virus (Pushko, P et al., 1997, Virology 239:389-401) vectors. These vaccines are self-replicating and self-limiting and may be administered as either RNA or DNA, which is then transcribed into RNA replicons in transfected cells or in vivo (Berglund et al., supra; Leitner, W W et al., 2000, Cancer Res. 60:51-55). Self-replicating RNA eventually causes lysis of transfected cells (Ying, H et al., 1999, Nat. Med. 5:823-827). These vectors do not raise the concern about integration into the host genome associated with naked DNA vectors. This is particularly important for development of vaccines that target potentially oncogenic proteins such as the human papillomavirus (HPV) E6 and E7 proteins.
One limitation on the potency of RNA replicon vaccines is their inability to spread in vivo. The present inventors conceived a strategy that facilitates the spread of antigen to enhance significantly the potency of RNA replicon vaccines.